Many personal care appliances, such as for example electric toothbrushes, are powered by replaceable batteries. One disadvantage of replaceable batteries is that battery voltage declines with discharge and use, with the voltage decreasing until the batteries finally die. Performance of the appliance begins to degrade significantly, however, well before the batteries actually die. Hence, there is a period of time during which, while the batteries are still operating, performance is adversely affected, which is undesirable. While all appliances with replaceable batteries have this functional disadvantage, even rechargeable batteries may have this disadvantage if their voltage declines between charging events.
It is thus desirable to be able to maintain battery voltage and thus consistent performance from replaceable and rechargeable batteries, above a specified threshold, in order to maintain a desired level of performance during the life of the appliance.